If I had the patience right now I'd tell you a story about that which my wife and I experienced back in a NJ Costco, but just to keep it short they DO even take back mostly eaten food. We stood in return line and the person in front of us made a return that unless you saw it you wouldn't believe it.
Also, return policy on TV & Computers (and some other electronic stuff) is 90 days because like with the food people took advantage of them so they changed it a few years ago. It's posted in all the stores.